DYNAMIC PROPERTIES OF GIANT COLLOIDAL SINGLE-CRYSTALS - DYNAMIC LIGHT-SCATTERING OF MONODISPERSED POLYSTYRENE SPHERES (192 NM IN DIAMETER) IN DEIONIZED SUSPENSION

Diffusive processes of colloidal ''gases'', ''liquids'' and ''crystals '' of monodispersed polystyrene spheres in an exhaustively deionized s uspension are investigated with a dynamic light scattering (DLS) techn ique. A single diffusive mode and then a single value of diffusion coe fficient D (or the effective diameter d(eff) derived from the coeffici ent) is evaluated for the ''gas-like'' suspensions from cumulant and h istogram analyses. D increases as the ionic concentration of the suspe nsion increases, this effect is due to a decrease in the width of the electrical double layers surrounding the spheres with increasing ionic strength. The intensity autocorrelation function for the ''liquid-lik e'' and ''crystal-like'' suspensions deviates greatly from the single exponential type of decay function. Generally, two or occasionally thr ee dynamical processes are observed for the colloidal liquids and crys tals from the histogram analyses. The fast and slow modes in the liqui ds are assigned to the quasi-synchronous fluctuation of spheres, and t o the restricted translational Brownian movement of spheres coated wit h the electrical double layers in the liquid cage. The fast mode of th e colloidal crystals may be assigned to the fast Brownian movement of spheres in a strongly interacting crystal lattice. The medium mode of fluctuation is assigned to the synchronous fluctuation of spheres and the surrounding electrical double layers in the crystal lattice, which is the main component among the two or three modes. The slow process is ascribed to the wave propagation of strains in the crystal lattice. D and d(eff) are rather independent of the scattering vector except f or crystal-like structures at: high sphere concentrations.